The present invention relates to an air control valve for controlling a flow rate of a fluid in response to an electric signal.
An air control valve for controlling a flow rate of air in response to an energizing current is provided in, for instance, an air passage used to bypass a throttle valve of an internal combustion engine. The air control valve is used to control an idling revolution number by controlling an air amount in response to a load of the internal combustion engine.
FIG. 5 is a sectional view of the conventional air control valve employed in such a use purpose, which is disclosed in, for example, Japanese Laid-open Patent Application No. 4-39475.
In this drawing, reference numeral 10 indicates a solenoid unit of the air control valve. The solenoid unit 10 is arranged by a bobbin 11, an energizing coil 12 wound on the bobbin 11, a cylindrical yoke 13 for covering an outer peripheral portion of the energizing coil 12, a fixed plate 14 and a side plate 15, which are provided at both end surfaces of these members and constitute a magnetic path. The solenoid unit 10 is stored into a cover 17, and is fixed by a synthetic resin filling member 16. Furthermore, a sleeve 18 made of a nonmagnetic material is inserted into the inner diameter portion of the bobbin 11 and fixed therein. A fixed core 19 fixed on the fixed plate 14, and a movable core 20 slidably provided in the sleeve 18 are inserted into the inner diameter portion of the sleeve 18. A return spring 22 supported by a spring washer (spring retainer) 21 of the fixed core 19 is provided between the fixed core 19 and the movable core 20, so that the movable core 20 is energized along a direction opposite to the attraction force caused by the energizing coil 12. Reference numeral 23 indicates an external lead line of the energizing coil 12, and reference numeral 24 shows a grommet.
Reference numeral 30 indicates a valve unit of the air control valve. The valve unit 30 includes a housing 34 and a valve body 35. The housing 34 is fitted and secured to a faucet unit 15a provided on the side plate 15 of the solenoid unit 10, and includes an air inlet port 31, an air outlet port 32, and the valve seat 33 formed in an air passage defined in an intermediate portion between the air inlet port 31 and the air outlet port 32. The valve body 35 constitutes a valve together with a valve seat 33 of the housing 34, and is slidably fitted into a small diameter portion 20a of the movable core 20. The valve body 35 is depressed against a drop preventing stopper 37 provided at a tip portion of the small diameter unit 20a by a spring 36 provided between the valve body 35 and the movable core 20. It should be noted that reference numeral 38 is an adjusting screw for adjusting the characteristic of the an control valve. The adjusting spring 38 is provided between the stopper 37 and a spring retainer 40 fixed to an adjusting screw 39 provided on the housing 34. The adjusting spring 38 energizes the movable core 20 along a direction opposite to the return spring 22.
In the conventional air control valve with the above-described structure, even when the valve is under full close condition, the valve body 35 is kept under such a condition of being depressed against the stopper 7, and the spring 36 functions as a buffering operation when the valve seat 33 and the valve body 35 are closed.
When no energizing current is supplied to the energizing coil 12, the movable core 20 closes the valve by way of the return spring 22, and the energizing current is supplied to the energizing coil 12 so that, the attraction force is exerted between the fixed core 19 and the movable core 20. When this attraction force reaches a difference between the force of the adjusting spring 38 and the force of the return spring 22 applied along the direction opposite to this attraction force, the valve starts to open. When the energizing current valve is further increased, the valve open degree based upon the valve of the energizing current flowing through the energizing coil 12, or the duty ratio of the current is maintained. The air will flow from the air inlet port 31 of the housing 34 to the air outlet port 32 thereof, and an amount of this air is defined based upon the energizing current, or the duty ratio of the current.
In such an air control valve, since the sleeve 18 for holding therein the fixed core 19 and the movable core 20 is required to be made of the nonmagnetic material and for the non-corrosive material, stainless steel is usually used to manufacture the sleeve 18 in the conventional air control valve. However, this may cause the cost-up factor in view of the manufacturing stages and the material cost. Also, anti-corrosion characteristic and high accuracy are required for the valve seat 33, the cut-machined member of a brass material is employed. This may also increase the manufacturing cost.
Furthermore, the movable core 20 slidably held in the sleeve 18 along the axial direction is slidable also along the rotation direction. As a result, when a circulation stream happens to occur in the air taken from the air inlet port 31, or vibrations are applied to the conventional valve itself during operation, the valve body 35 would be rotated, so that there is a change in the relative position between the valve seat 33 and the valve body 35. In particular, when the valve open degree is low, the valve open degree characteristic with respect to the current value would be varied, and thus the revolution control would be brought into malfunction.
Furthermore, there are other problems that when the vibrations produced while the valve is fully open, and the over current are applied, the movable core 20 would collide with the fixed core 19, resulting in deterioration of durability.